This invention relates generally to microwave devices and more particularly to microwave reflection amplifiers.
As is known in the art, a microwave reflection amplifier includes negative resistance devices such as IMPATT diodes, disposed in resonant circuits which are passively power combined to provide higher output power. The passive power combiner also matches the active device resonant circuit impedance to the impedance of an external load. The reflection amplifier has input waves and output waves sharing the same port (i.e. the I/O port) of the amplifier. An input wave fed to the I/O port is split by the passive power combiner and propagates towards each of the negative resistance devices, whereas the output waves which are amplified versions of the input waves propagate away from each of the negative resistance devices to the power combiner where they are combined to provide a high power output wave.
The bandwidth of a reflection amplifier is determined primarily by the frequency range over which the microwave resonant circuit can generate the proper load impedance for the active device. In general, reflection amplifiers will have the highest gain at a single frequency, and the gain will drop off or "roll off" sharply as frequency varies above or below this single frequency. For a narrow band application, this rolloff in frequency is small and acceptable. However, for higher bandwidths on the order of 5% or more, for example, this "roll off" is appreciable and undesireable. Therefore, for negative resistance devices, it is difficult to obtain a large bandwidth from such a microwave circuit. Accordingly, a technique is required to increase the bandwidth of narrow band devices such as IMPATT diodes when incorporated in reflection amplifiers.